JP2009512548A - Removal of carbon dioxide from absorbent and gas streams. - Google Patents

Abstract

を表し、かつ他の基Ｒは水素を表す］のアミンの水溶液を含有する、ガス流から二酸化炭素を除去するための吸収剤が記載されている。該吸収剤は特別な酸化安定性が傑出している。Formula (I) wherein one or two groups R are

And the other group R represents hydrogen], an absorbent for removing carbon dioxide from a gas stream is described. The absorbents stand out for their special oxidation stability.

Description

  The present invention relates to an absorbent for removing carbon dioxide from a gas stream and a method using the absorbent.

In many processes in the chemical industry, acid gases, for example _{CO 2, H 2 S, SO} 2, CS 2, HCN, COS, fluid streams containing NO _x, a disulfide or a mercaptan as impurities occurs. The fluid stream can be, for example, a gas stream, such as natural gas, synthesis gas, refinery gas, or organic materials such as organic waste, coal, natural gas or petroleum, or waste containing organic substances. It is a reaction gas generated during composting.

  Removal of acid gas is particularly important for various reasons. For example, the sulfur content of natural gas must be reduced in the immediate vicinity of the natural gas source by appropriate post-treatment measures, since sulfur compounds also form acids with water often associated with natural gas. However, this acid has a corrosive action. Therefore, in order to transport natural gas by pipeline, certain limits for sulfur-containing impurities must be observed. In order to avoid the release of gases that can harm nature or affect the environment, the acid gas must be removed from the reaction gas produced during the oxidation of the organic material.

  On an industrial scale, often an aqueous solution of an organic base, such as an alkanolamine, is used as an absorbent. When the acid gas is dissolved, an ionic product is formed from the base and the acid gas component. The absorbent can be regenerated by releasing or stripping to a relatively low pressure, wherein the acid gas is liberated again and / or stripped using steam. The absorbent can be reused after the regeneration process.

  The known absorbents are very well suited for the deoxidation of hydrocarbon streams such as natural gas. Certain problems arise in the treatment of oxygen-containing fluids such as flue gas. At that time, the absorbent capacity of the absorbent deteriorates over a long period of time and is not completely recovered during regeneration. Presumably, the presence of molecular oxygen is responsible for the oxidative degradation of amines contained in the absorbent.

  The present invention is based on the problem of showing an absorbent that retains the absorbent capacity of the absorbent over a long period of time and a method of deoxidizing the fluid stream.

を表し、かつ他の基Ｒは水素を表す］
のアミンの水溶液を含有する吸収剤により解決される。 The above problem is solved by formula I
HNR ₂ (I)
[Where:
One or two radicals R are

And the other group R represents hydrogen]
This is solved by an absorbent containing an aqueous solution of an amine.

  In one embodiment, the compound of formula I is 1-amino-2-methyl-propan-2-ol (CAS 2854-16-2; hereinafter: 1A2MP). In another embodiment, amino-di-tert-butyl alcohol. Both compounds have been found to exhibit surprisingly high oxygen stability.

  The first step of decomposition induced by molecular oxygen is probably the extraction of a hydrogen atom from a carbon atom that is alpha to the amino group. Amines in which the α-carbon atom exclusively has substituents other than hydrogen are extremely stable against oxidative degradation. In 1A2MP, the carbon atom in the α-position to the amino group is a primary carbon atom, that is, this carbon atom has two hydrogen atoms. Surprisingly, however, this structure was found to be extremely stable against the action of molecular oxygen. Since stability against oxygen-induced decomposition is particularly important for flue gas scrubbing, the new absorbent here is a great improvement.

  For example, in order to optimize the loading force of carbon dioxide or other acid gas components on the absorbent, the mass transfer rate and / or other factors related to carbon dioxide or other acid gas components, the absorbent according to the present invention is of formula I In addition to the amine, one or more other amines may be included. These or other amines usually contain 4 to 12 carbon atoms.

  The absorbent is usually present in the form of an aqueous solution having a total amine content of generally 10 to 65% by weight, preferably 25 to 60% by weight. The amines of the formula I are generally assigned at least 1% by weight, preferably at least 5% by weight, based on the absorbent.

  In addition to water, the solution may contain a physical solvent, such as cyclotetramethylene sulfone (sulfolane) and its derivatives, aliphatic acid amides (acetylmorpholine, N-formylmorpholine), N-alkylated. It is selected from pyrrolidone and the corresponding piperidones such as N-methylpyrrolidone (NMP), propylene carbonate, methanol, dialkyl ethers of polyethylene glycol and mixtures thereof.

  The absorbent according to the invention may further contain functional components such as stabilizers, in particular antioxidants. See for example DE102004011427. The addition of an acid, such as phosphoric acid, formic acid or sulfonic acid, may be suitable to reduce the energy required for regeneration of the loaded absorbent.

Suitable amines that may be present in the absorbent according to the invention in addition to the amine of the formula I are, for example, (A) tertiary amines (hereinafter referred to as tertiary monoamines or polyamines having exclusively tertiary amino groups). );
(B) a primary amine, wherein the amino group is attached to a tertiary carbon atom;
(C) a secondary amine, wherein the amino group is bound to at least one secondary or tertiary carbon atom;
And mixtures thereof.

Preferred amines are: (A) tertiary amines having 3 hydroxyalkyl groups on the nitrogen atom, wherein the amino group is separated from the hydroxyl group by at least 2 carbon atoms, For example triethanolamine (TEA);
A tertiary amine having one or two hydroxyalkyl groups and two or one unsubstituted alkyl groups on the nitrogen atom, wherein the amino group is at least two carbon atoms and one or more hydroxyl groups For example, diethylethanolamine (DEEA), methyldiethanolamine (MDEA), 3-dimethylamino-1-propanol (DIMAP), dimethylethanolamine (DMEA), methyldiisopropanolamine (MDIPA);
A diamine having two tertiary amino groups;
For example, N, N, N ′, N′-tetramethylethylenediamine, N, N-diethyl-N ′, N′-dimethylethylenediamine, N, N, N ′, N′-tetraethylethylenediamine, N, N, N ′, N′-tetramethyl-1,3-propanediamine and N, N, N ′, N′-tetraethyl-1,3-propanediamine and bis (dimethylaminoethyl) ether,
(B) a primary amine having at least one hydroxyl group, wherein the amino group is bonded to a tertiary carbon atom and is separated from the hydroxyl group by at least two carbon atoms;
For example, 2-amino-2-methyl-1-propanol (AMP), 3-amino-3-methyl-2-pentanol, 2,3-dimethyl-3-amino-1-butanol, 2-amino-2-ethyl -1-butanol, 2-amino-2-methyl-3-pentanol, 2-amino-2-methyl-1-butanol, 3-amino-3-methyl-1-butanol, 3-amino-3-methyl- 2-butanol, 2-amino-2,3-dimethyl-3-butanol, 2-amino-2,3-dimethyl-1-butanol and 2-amino-2-methyl-1-pentanol, of which 2- Amino-2-methyl-1-propanol is preferred;
(C) a secondary amine having at least one hydroxyl group, wherein the amino group is bound to at least one secondary or tertiary carbon atom and separated from the hydroxyl group by at least two carbon atoms Assuming that
For example, 2- (isopropylamino) ethanol, 2 (sec-butylamino) ethanol, 2-piperidineethanol;
And mixtures thereof.

Advantageous absorbents are each below the total mass of the absorbent:
(I) 1 to 30%, preferably 5 to 25%, and (ii) one or more amines (A) to (C) 10 to 60%, preferably 15 to 50%, by weight of amine of formula I ,
However, the maximum total amine content of the absorbent is 65% by weight,
Containing.

In another embodiment, the absorbent according to the invention comprises, in addition to the amine of formula I, the following (D) primary or secondary alkanolamine:
(E) alkylene diamine;
(F) polyalkylene polyamine;
(G) Formula R ¹ —NH—R ² —NH ₂
[Where:
R ¹ represents C ₁ -C ₆ alkyl and R ² represents C ₂ -C ₆ alkylene]
Amines of
(H) a cyclic amine having a 5-membered, 6-membered or 7-membered saturated ring containing an NH group and optionally another heteroatom, in particular one oxygen atom or nitrogen atom;
And at least one amine selected from the mixtures thereof.

Particularly suitable amines are: (D) monoethanolamine (MEA), diethanolamine (DEA), diisopropylamine (DIPA), aminoethoxyethanol (AEE);
(E) hexamethylenediamine;
(F) diethylenetriamine; triethylenetetramine, 3,3-iminobispropylamine; preferably diethylenetriamine;
(G) 3-methylaminopropylamine (MAPA);
(H) piperazine, 2-methylpiperazine, N-methylpiperazine, N-ethylpiperazine, N-aminoethylpiperazine, homopiperazine, piperidine, morpholine;
And mixtures thereof.

Advantageous absorbents are each below the total mass of the absorbent:
(I) 20 to 60% by weight, preferably 25 to 50% by weight, of the amine of formula I, and (ii) one or more amines (D) to (H) 1 to 25% by weight, preferably 3 to 20% by weight
However, the maximum total amine content of the absorbent is 65% by weight,
Containing.

  The present invention also relates to a method for removing carbon dioxide from a gas stream, wherein the gas stream is contacted with a liquid absorbent containing an aqueous solution of an amine of formula I.

In addition to carbon dioxide, other acid gases and / or precursor compounds thereof, such as H ₂ S, SO ₂ , CS ₂ , HCN, COS, NO _x , disulfides or mercaptans are partially or completely removed from the gas stream. .

  The process is particularly suitable for gas streams in which the partial pressure of carbon dioxide in the gas stream is less than 500 mbar, preferably less than 200 mbar, usually 20 to 150 mbar.

The gas stream is preferably formed by the following methods a) oxidation of organic substances, for example flue gas (flue gas) b) composting and storage of waste containing organic substances, or c) bacterial decomposition of organic substances Gas flow.

  The oxidation may be carried out under a flame phenomenon, ie as a conventional combustion or as an oxidation without a flame phenomenon, for example in the form of catalytic oxidation or partial oxidation. The organic material subjected to combustion is usually a fossil fuel, such as coal, natural gas, petroleum, gasoline, diesel oil, raffinate or kerosene, biodiesel oil or waste containing organic material. The starting material for catalytic (partial) oxidation is, for example, methanol or methane which can be converted to formic acid or formaldehyde.

  The waste that is subjected to oxidation, composting or storage is typically household waste, plastic waste or packaging waste.

  The combustion of organic substances is often performed using air in a conventional combustion apparatus. Composting and storage of waste containing organic materials is generally performed in a garbage dump. The exhaust gas or exhaust of such a plant can advantageously be treated by the method according to the invention.

  As organic substances for bacterial degradation, fertilizer, straw, manure, sewage sludge, fermentation residue, etc. are usually used. Bacterial degradation is performed, for example, in a conventional biogas apparatus. The exhaust from such a plant can advantageously be treated by the method according to the invention.

  The method is suitable for exhaust gas treatment of fuel cells or chemical synthesis plants used for (partial) oxidation of organic substances.

  Along with it, the method according to the invention is of course used to treat unburned fossil gas, for example natural gas, for example so-called coal bed gas, i.e. the collected and compressed gas produced when mining coal. Also good.

Generally, the gas stream contains less than 50 mg / m ^{3 of} sulfur dioxide under standard conditions.

  The starting gas can have an ambient air pressure, i.e. a pressure approximately corresponding to normal pressure, for example, or a pressure up to 1 bar away from normal pressure.

  Suitable devices for carrying out the process according to the invention include at least one scrubber tower, such as irregular packed towers, ordered packed towers and plate towers and / or other absorbers, such as membrane contactors, radial flow scrubbers, jets Includes scrubbers, venturi scrubbers and rotary spray scrubbers. Here, the treatment of the gas stream with the absorbent is preferably carried out countercurrently in the scrubber tower. The gas stream is generally fed to the lower region and the absorbent is fed to the upper region of the tower.

  Also suitable for carrying out the process according to the invention are scrubber towers made of plastic, for example polyolefins or polytetrafluoroethylene, or scrubber towers whose inner surface is wholly or partly covered with plastic or rubber. Furthermore, a membrane contactor with a plastic casing is suitable.

  The temperature of the absorbent is generally about 30 to 70 ° C. in the absorption step. When a tower is used, it is, for example, 30 to 60 ° C. at the top of the tower and 40 to 70 ° C. at the bottom of the tower. A product gas (by-product gas) depleted of the acidic gas component, that is, this component is reduced, and an absorbent loaded with the acid gas component are obtained.

  Carbon dioxide may be liberated in the regeneration process from the absorbent loaded with acidic gas components, resulting in a regenerated absorbent. In the regeneration process, the load of the absorbent is reduced and the resulting regenerated absorbent is advantageously subsequently returned to the absorption process.

In general, the loaded absorbent is a) heated to, for example, 70-120 ° C.
b) pressure release,
c) Regenerated by stripping with inert fluid or a combination of two or all of the above methods.

  In general, the loaded absorbent is heated for regeneration and the liberated carbon dioxide is separated, for example, in a desorption tower. Before the regenerated absorbent is again introduced into the absorber, the absorbent is cooled to a suitable absorption temperature. In order to utilize the energy contained in the absorbent regenerated at high temperature, it is advantageous to preheat the loaded absorbent from the absorber by heat exchange with the absorbent regenerated at high temperature. Because heat exchange brings the loaded absorbent to a higher temperature, the regeneration process requires less energy usage. Already by heat exchange, partial regeneration of the loaded absorbent can take place under the release of carbon dioxide. The resulting gas-liquid mixed phase stream is introduced into a phase separation vessel and carbon dioxide is removed from this phase separation vessel; the liquid phase is introduced into the desorption tower for complete regeneration of the absorbent.

  Often, the carbon dioxide liberated in the desorption tower is subsequently compressed and fed, for example, to a pressure tank or a sequestering section. In this case, it is advantageous to carry out the regeneration of the absorbent at a relatively high pressure, for example 2 to 10 bar, preferably 2.5 to 5 bar. For this purpose, the loaded absorbent is compressed to the regeneration pressure by the pump and introduced into the desorption tower. Carbon dioxide is thus generated at relatively high pressure levels. The pressure difference from the pressure level of the pressure tank is relatively small, and in some cases, the compression process can be omitted. Due to the relatively high pressure during regeneration, the regeneration temperature is relatively high. If the regeneration temperature is relatively high, a relatively small residual load of the absorbent can be achieved. The regeneration temperature is generally limited only by the thermal stability of the absorbent.

  In order to cool and wet (quenching) the flue gas, the flue gas is preferably subjected to washing with an aqueous liquid, in particular water, before the absorbent treatment according to the invention. In the case of cleaning, dust or gaseous impurities such as sulfur dioxide can also be removed.

  The present invention will be described in detail with reference to the accompanying drawings and the following examples.

  FIG. 1 is a schematic view of an apparatus suitable for carrying out the method according to the invention.

According to FIG. 1, the carbon dioxide-containing combustion gas appropriately pretreated via the supply pipe 1 is in countercurrent with the regenerated absorbent supplied via the absorbent conduit 3 in the absorber 2. Touched. The absorbent removes carbon dioxide by absorption from the combustion gas; here, pure gas depleted of carbon dioxide is obtained via the exhaust pipe 7. The absorption device 2 can have a backwash tray or backwash section (not shown), preferably equipped with a filling, above the absorbent inlet, in which the backwash tray or backwash section The absorbent, which is led together by water or condensate, is separated from the gas with a reduced CO ₂ content. The liquid on the backwash tray is appropriately recirculated through an external cooler.

Absorbent conduit 5, pump 12, solvent-solvent-heat exchanger 11 (in this heat exchanger, the heat of the regenerated absorbent from which the absorbent loaded with acid gas flows out from the bottom of the desorption tower 7 The absorbent loaded with carbon dioxide is supplied to the desorption tower 7 through the throttle valve 6. In the lower part of the desorption tower 7, the loaded absorbent is heated and regenerated by a heater (not shown). The carbon dioxide released at this time leaves the desorption tower 7 via the exhaust gas pipe 8. The desorption tower 7 can have a backwash tray or backwash section (not shown), preferably equipped with a packing, above the absorbent inlet, in which the backwash tray or backwash section Absorbents that are led together by water or condensate are separated from the liberated CO ₂ . The conduit 8 may be provided with a heat exchanger having a top distributor or condenser. Subsequently, the regenerated absorbent is pumped to a solvent-solvent-heat exchanger 11 (in the heat exchanger, the regenerated absorbent heats the absorbent loaded with acid gas, where it Cooling itself) and supplied again to the absorption tower 2 via the heat exchanger 10. The portion of the absorbent removed from the desorption tower 7 in order to avoid the accumulation of absorbed material that is not ejected or completely ejected during regeneration or the accumulation of decomposition products in the absorbent. A stream can be fed to the evaporator, in which less volatile by-products and decomposition products are formed as residues and the pure absorbent is removed as a vapor. The condensed vapor is supplied again to the absorbent circuit. If appropriate, a base, for example potassium hydroxide, can be added to the partial stream, which base forms, for example, a refractory salt with sulfate or chloride ions, which refractory salt together with the evaporator residue. It is taken out from the system.

Examples The stability of various amines against the action of oxygen was measured as follows:
In a 100 ml flask, about 60 ml of amine was bubbled through a frit at ambient pressure for 6 days at 120 ° C. with 5 l of air (STP) / h. The vapor space above the solution was inactivated with 10 ₂ N ₂ (STP) / h. The flask was equipped with a reflux condenser, which fully condensed and returned the stripped material.

  Samples of fresh solution and solution treated for 6 days were taken and analyzed by GC.

GC method: 30 m RTX-5 amine (0.32 mm, 1.5 μm), 50 ° C.-3 minutes, −7 ° C./min.
2-Amino-2-methyl-propan-1-ol (comparison)
Concentration of original solution: 93.5%
Concentration after 6 days test: 93.4%
Sample 2:
1-amino-2-methyl-propan-2-ol Concentration of original solution: 99.8%
Concentration after 6 days test: 98.2%
Sample 3:
Monoethanolamine (comparison)
Original solution concentration: 100%
Concentration after 6 days test: 32.8%
Sample 4:
Methyldiethanolamine (comparison)
Concentration of original solution: 99.3%
Concentration after 6 days test: 72.4%
Sample 5:
Methyl monoethanolamine (comparison)
Concentration of original solution: 99.6%
Concentration after 6 days test: 75.5%

1 is a schematic view of an apparatus suitable for carrying out the method according to the invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Supply pipe, 2 Absorber, 3 Absorber conduit, 5 Absorbent conduit, 6 Throttle valve, 7 Desorption tower, 8 Exhaust gas pipe, 9 Pump, 10 Heat exchanger, 11 Heat exchanger, 12 Pump

Claims (11)

In an absorbent for removing carbon dioxide from a gas stream, the formula I
HNR ₂ (I)
[Where:
One or two radicals R are

And the other group R represents hydrogen]
An absorbent comprising an aqueous solution of an amine. Further, (A) a tertiary amine;
(B) a primary amine, wherein the amino group is attached to a tertiary carbon atom;
(C) a secondary amine, wherein the amino group is bound to at least one secondary or tertiary carbon atom;
And an at least one amine selected from the mixtures thereof. (A) a tertiary amine having one or two hydroxyalkyl groups and two or one unsubstituted alkyl groups on the nitrogen atom, wherein the amino group is one or more by at least two carbon atoms Is separated from the hydroxyl group of
(B) a primary amine having at least one hydroxyl group, wherein the amino group is attached to a tertiary carbon atom and is separated from the hydroxyl group by at least two carbon atoms;
(C) a secondary amine having at least one hydroxyl group, wherein the amino group is bound to at least one secondary or tertiary carbon atom and separated from the hydroxyl group by at least two carbon atoms Shall be;
And at least one amine selected from the mixtures thereof and the absorbent according to claim 2.   Contains 1-30% by weight of the amine of formula I and 10-60% by weight of one or more amines (A)-(C), based on the total weight of the absorbent, provided that the largest total amine of the absorbent The absorbent according to claim 2 or 3, wherein the content is 65% by mass. Further, (D) primary or secondary alkanolamine:
(E) alkylene diamine;
(F) polyalkylene polyamine;
(G) Formula R ¹ —NH—R ² —NH ₂
[Where:
R ¹ represents C ₁ -C ₆ alkyl and R ² represents C ₂ -C ₆ alkylene]
Amines of
(H) a cyclic amine having a 5-membered, 6-membered or 7-membered saturated ring containing an NH group and optionally another heteroatom, in particular one oxygen atom or nitrogen atom;
And an at least one amine selected from the mixtures thereof. The following (D) monoethanolamine, diethanolamine, methylethanolamine;
(E) hexamethylenediamine;
(F) diethylenetriamine;
(G) 3-methylaminopropylamine;
(H) piperazine, 2-methylpiperazine, N-methylpiperazine, N-ethylpiperazine, N-aminoethylpiperazine, homopiperazine, piperidine, morpholine;
And at least one amine selected from said mixtures thereof.   Contains 20 to 60% by weight of the amine of formula I and 1 to 25% by weight of one or more amines (D) to (H), based on the total weight of the absorbent, provided that the largest total amine of the absorbent The absorbent according to claim 5 or 6, wherein the content is 65% by mass. In a method for removing carbon dioxide from a gas stream, the gas stream is represented by the formula I
HNR ₂ (I)
[Where:
One or two radicals R are

And the other group R represents hydrogen]
Contacting with a liquid absorbent containing an aqueous solution of the amine.   9. A process according to claim 8, wherein the partial pressure of carbon dioxide in the gas stream is less than 500 mbar. 10. A method according to claim 8 or 9, wherein the gas stream is derived from a) oxidation of organic material b) composting or storage of waste containing organic material, or c) bacterial degradation of organic material. 11. The loaded absorbent is regenerated by: a) heating b) releasing pressure c) stripping with an inert fluid or a combination of two or all of the above methods. the method of.

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